A voltage step up/down circuit known in the art includes a ring oscillator, a charge pump, and a regulator. According to this type of voltage step up/down circuit, an oscillation signal generated by the ring oscillator is stepped up or down by using the charge pump, and is set to a desired voltage by using the regulator.
The capability of voltage step up and down may be increased by increasing the consumption current of an output buffer contained in the ring oscillator. However, this output buffer allows constant flow of a current even after coming into a steady state, and therefore consumes unnecessary current.